Vertical semiconductor device and method for fabricating the same

ABSTRACT

A semiconductor device includes: an alternating stack that is disposed over a lower structure and includes gate electrodes and dielectric layers which are staked alternately; a memory stack structure that includes a channel layer extending to penetrate through the alternating stack, and a memory layer surrounding the channel layer; a source contact layer in contact with a lower outer wall of the vertical channel layer and disposed between the lower structure and the alternating stack; a source contact plug spaced apart from the memory stack structure and extending to penetrate through the alternating stack; and a sealing spacer suitable for sealing the gate electrodes and disposed between the source contact plug and the gate electrodes. The sealing spacer has an etch resistance that is different from an etch resistance of the dielectric layers.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is the continuation of U.S. application Ser. No.16/842,141 filed Apr. 7, 2020 and claims priority of Korean PatentApplication No. 10-2019-0156872, filed on Nov. 29, 2019, which isincorporated herein by reference in its entirety.

BACKGROUND 1. Field

Embodiments of the present disclosure relate to a semiconductor device,and more particularly, to a method for fabricating a verticalsemiconductor device.

2. Description of the Related Art

Fabrication of electronic devices such as semiconductor devices includesa gapfill process for forming a three-dimensional structure or a highaspect ratio structure. The gapfill process to form a high aspect ratiostructure is performed, for example, in the fabrication of a verticalsemiconductor device.

SUMMARY

Embodiments of the present disclosure are directed to a verticalsemiconductor device with improved reliability, and a method forfabricating the vertical semiconductor device.

In accordance with an embodiment of the present disclosure, asemiconductor device includes: an alternating stack that is disposedover a lower structure and includes gate electrodes and dielectriclayers which are staked alternately; a memory stack structure thatincludes a channel layer extending to penetrate through the alternatingstack, and a memory layer surrounding the channel layer; a sourcecontact layer in contact with a lower outer wall of the vertical channellayer and disposed between the lower structure and the alternatingstack; a source contact plug spaced apart from the memory stackstructure and extending to penetrate through the alternating stack; anda sealing spacer suitable for sealing the gate electrodes and disposedbetween the source contact plug and the gate electrodes, the sealingspacer having an etch resistance that is different from an etchresistance of the dielectric layers.

In accordance with another embodiment of the present disclosure, amethod for fabricating a semiconductor device includes: forming a sourcesacrificial layer over a lower structure; forming a multi-layer stack inwhich dielectric layers and sacrificial layers are alternately stackedover the source sacrificial layer; forming a memory stack structure thatincludes a channel layer and a memory layer, the memory stack structureextending to penetrate through the multi-layer stack and the sourcesacrificial layer; forming a vertical contact recess that is spacedapart from the memory stack structure and extends to penetrate throughthe multi-layer stack and the source sacrificial layer; exposing a lowerouter wall of the channel layer by selectively removing the sourcesacrificial layer and a lower portion of the memory layer of the memorystack structure through the vertical contact recess; forming a sourcecontact layer that surrounds the lower outer wall of the channel layer;replacing the sacrificial layers of the multi-layer stack with gateelectrodes to form an alternating stack; forming a carbon-containingspacer to seal a sidewall of the vertical contact recess over the sourcecontact layer and the gate electrodes; and forming a source contact plugin the vertical contact recess.

In accordance with another embodiment of the present disclosure, amethod for fabricating a semiconductor device includes: forming a firstmulti-layer stack including liner layers and a source sacrificial layerover a lower structure; forming a second multi-layer stack includingdielectric layers and sacrificial layers over the first multi-layerstack; forming a vertical contact recess extending through the secondmulti-layer stack and the source sacrificial layer; replacing the sourcesacrificial layer with a source contact layer; forming acarbon-containing spacer on sidewall of the vertical contact recess;replacing the sacrificial layers with conductive layers; and forming asource contact plug in the vertical contact recess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a vertical semiconductordevice in accordance with an embodiment of the present disclosure.

FIGS. 2 to 14 are cross-sectional views illustrating a method forfabricating a vertical semiconductor device in accordance with anembodiment of the present disclosure.

FIG. 15 is a cross-sectional view illustrating a vertical semiconductordevice in accordance with another embodiment of the present disclosure.

FIGS. 16 to 28 are cross-sectional views illustrating a method forfabricating a vertical semiconductor device in accordance with anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described below in moredetail with reference to the accompanying drawings. Embodiments of thepresent disclosure may, however, be implemented in different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of variousembodiments of the present disclosure to those skilled in the art.Throughout the disclosure, like reference numerals refer to like partsthroughout the various figures and embodiments of the presentdisclosure.

The drawings are not necessarily to scale and in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When a first layer is referred to as being“on” a second layer or “on” a substrate, it not only refers to a casewhere the first layer is formed directly on the second layer or thesubstrate but also a case where a third layer exists between the firstlayer and the second layer or the substrate.

FIG. 1 is a cross-sectional view illustrating a vertical semiconductordevice 100 in accordance with an embodiment of the present disclosure.

Referring to FIG. 1, the vertical semiconductor device 100 may bepositioned over a lower structure 101, and the vertical semiconductordevice 100 may include an alternating stack 120 in which dielectriclayers 111 and gate electrodes 127 are alternately stacked, a memorystack structure 120P including a channel layer 118 extending topenetrate the alternating stack 120 and a stack of layers (or a memorylayer) 115, 116, and 117 surrounding the channel layer 118, a sourcecontact layer 124 disposed between the lower structure 101 and thealternating stack 120 while contacting an outer wall of a bottom portionof the channel layer 118, a source contact plug 132 spaced apart fromthe memory stack structure 120P and extending through the alternatingstack 120, and a sealing spacer 128 having a different etch resistancefrom that of the dielectric layers 111 while sealing an outer wall ofthe source contact plug 132. The sealing spacer 128 may seal the gateelectrodes 127 and be disposed between the source contact plug 132 andthe gate electrodes 127, and may have different etch resistance from thedielectric layers 111. The outer wall of the source contact plug 132 maybe surrounded by the sealing spacer 128, and the sealing spacer 128 mayvertically extend to cover the gate electrodes 127, the dielectriclayers 111, and the source contact layer 124.

The lower structure 101 may include a material suitable forsemiconductor processing. The lower structure 101 may include asubstrate, and the substrate may include a semiconductor substrate. Forexample, the lower structure 101 may be a silicon substrate, amonocrystalline silicon substrate, a polysilicon substrate, an amorphoussilicon substrate, a silicon germanium substrate, a monocrystallinesilicon germanium substrate, a polycrystalline silicon germaniumsubstrate, a carbon-doped silicon substrate, a combination thereof, or amulti-layer thereof. The lower structure 101 may include othersemiconductor materials, such as germanium. The lower structure 101 mayinclude a III/V-group semiconductor substrate, such as a compoundsemiconductor substrate, e.g., GaAs. The lower structure 101 may includea Silicon-On-Insulator (SOI) substrate. Although not shown, according toanother embodiment of the present disclosure, the lower structure 101may include a substrate, at least one control circuit formed over thesubstrate, and a multi-layer metal line.

A multi-layer stack structure may be formed over the lower structure101. The multi-layer stack structure may include a source-level stack110 and an alternating stack 120 over the source-level stack 110. Thesource-level stack 110 may have a height lower than a height of thealternating stack 120.

The source-level stack 110 may include a lower source layer 102, asource contact layer 124, and an upper source layer 106. The sourcecontact layer 124 may be formed over the lower source layer 102, and theupper source layer 106 may be formed over the source contact layer 124.The source contact layer 124 may be disposed between the lower sourcelayer 102 and the upper source layer 106. The lower source layer 102,the upper source layer 106, and the source contact layer 124 may includea semiconductor material. The lower source layer 102, the upper sourcelayer 106, and the source contact layer 124 may include polysilicon. Thesource contact layer 124 may include polysilicon doped with phosphorus(P). The source contact layer 124 may include polysilicon containingcarbon. The source contact layer 124 may include a stack ofphosphorus-doped polysilicon (SiP) and carbon-doped polysilicon (SiC).The lower source layer 102 and the upper source layer 106 may includeundoped polysilicon or doped polysilicon.

The alternating stack 120 may be referred to as a memory cell stack or amemory cell string. The alternating stack 120 may have a structure inwhich a plurality of dielectric layers 111 and a plurality of gateelectrodes 127 are alternately stacked. The top dielectric layer 113among the dielectric layers 111 may be thicker than the dielectriclayers 111 at lower levels than the top dielectric layer 113. Thedielectric layers 111 may include silicon oxide. The gate electrodes 127may include a low-resistance material. The gate electrodes 127 mayinclude a metal-based material. The gate electrodes 127 may includemetal, metal silicide, metal nitride, or a combination thereof. Forexample, the metal may include nickel, cobalt, platinum, titanium,tantalum, or tungsten. The metal silicide may include nickel silicide,cobalt silicide, platinum silicide, titanium silicide, tantalumsilicide, or tungsten silicide. The gate electrodes 127 may include astack of titanium nitride and tungsten. The ends of the gate electrodes127 may have a shape that is horizontally recessed from the ends of thedielectric layers 111.

The memory stack structure 120P may extend vertically to penetratethrough the alternating stack 120. The memory stack structure 120P mayhave a pillar shape. The memory stack structure 120P may include ablocking layer 115, a charge trapping layer 116, a tunnel dielectriclayer 117, a channel layer 118, and a core dielectric layer 119. Thememory stack structure 120P may include an ONOP structure. The ONOPstructure may include a stack of oxide, nitride, oxide, and polysiliconlayers. The blocking layer 115 and the tunnel dielectric layer 117 mayinclude an oxide, and the charge trapping layer 116 may include anitride, and the channel layer 118 may include polysilicon. According toan embodiment of the present disclosure, the blocking layer 115 mayinclude a high dielectric material, and the high dielectric material mayinclude aluminum oxide or hafnium oxide. The channel layer 118 may havea cylindrical shape having an inner space. The tunnel dielectric layer117 may be formed on the outer wall of the channel layer 118, and thecharge trapping layer 116 may be formed on the outer wall of the tunneldielectric layer 117. The blocking layer 115 may be formed on the outerwall of the charge trapping layer 116. The inner space of the channellayer 118 may be substantially completely filled with the coredielectric layer 119. The core dielectric layer 119 may include siliconoxide or silicon nitride. The stack of the blocking layer 115, thecharge trapping layer 116, and the tunnel dielectric layer 117 may bereferred to as a memory layer 115/116/117, which may be of an annularshape surrounding the outer wall of the channel layer 118.

The source contact layer 124 may selectively horizontally penetratethrough a bottom portion of the memory layer 115/116/117 of the memorystack structure 120P to contact the lower outer wall of the channellayer 118. The source contact layer 124 may have a shape surrounding thelower outer wall of the channel layer 118.

The source contact plug 132 may include a stack of thesilicon-containing material (or the silicon-containing material pattern)129 and the metal-containing material (or the metal-containing materialpattern) 131, and may further include a barrier material (or a barriermaterial layer) 130 between the silicon-containing material 129 and themetal-containing material 131. The silicon-containing material 129 mayinclude polysilicon, and the metal-containing material 131 may includetungsten. The barrier material 130 may include titanium nitride.According to another embodiment of the present disclosure, the sourcecontact plug 132 may be formed of tungsten alone. The lower portion ofthe source contact plug 132 may be coupled to the lower source layer 102of the source-level stack 110.

The sealing spacer 128 may be formed between the source contact plug 132and the gate electrodes 127. The sealing spacer 128 may extend to beformed between the dielectric layers 111 and 113 and the source contactplug 132. For example, the sealing spacer 128 may extend along thevertical direction in which the gate electrodes 127 and the dielectriclayers 111 and 113 of the alternating stack 120 are stacked, such thatthe sealing spacer 128 may be disposed between the source contact plug132 and the dielectric layers 111 and 113. The sealing spacer 128 may becontinuous in the stacking direction of the alternating stack 120. Thesealing spacer 128 may include one or more protrusions 128P, and theprotrusions 128P may be coupled to the ends (e.g., ends 127R in FIG. 10)of the gate electrodes 127, respectively. The protrusions 128P of thesealing spacer 128 may extend in the horizontal direction that isperpendicular to the stacking direction of the alternating stack 120.The protrusions 128P of the sealing spacer 128 may seal the recessedends of the gate electrodes 127. The sealing spacer 128 may seal thesides of the dielectric layers 111 and 113. The sealing spacer 128 mayseal the sides of the source contact layer 124. The sealing spacer 128may seal the side of the upper source layer 106 and may not seal aportion of the surface of the lower source layer 102. The sealing spacer128 may substantially fully surround the outer wall of the sourcecontact plug 132.

The sealing spacer 128 may include a silicon oxide-based material. Thesealing spacer 128 may include a low dielectric material. The lowdielectric material may have a lower dielectric constant than siliconnitride. The sealing spacer 128 may have a dielectric constant lowerthan approximately 7. The sealing spacer 128 may be thinner than thedielectric layers 111 and 113 and the gate electrodes 127. In theembodiment shown in FIG. 1, the sealing spacer 128 may have a thicknessin the horizontal direction smaller than a thickness of each of thedielectric layers 111 and 113 and the gate electrodes 127 in thevertical direction. For example, a thickness of the protrusion 128P ofthe sealing spacer 128 in the horizontal direction may be smaller than athickness of each of the dielectric layers 111 and 113 and the gateelectrodes 127 in the vertical direction. The sealing spacer 128 may bea layer of a material that is different from those of the dielectriclayers 111 and 113. The sealing spacer 128 may be a layer of a materialthat is different from those of the gate electrodes 127. The sealingspacer 128 may include a material having a high wet-etch resistance. Thewet-etch resistance of the sealing spacer 128 may be obtained fromcarbon. The sealing spacer 128 may include a carbon-containing material,and the dielectric layers 111 and 113 may be a carbon-free material. Thedielectric layers 111 and 113 may be formed of carbon-free siliconoxide, and the sealing spacer 128 may be formed of carbon-containingsilicon oxide. For example, the dielectric layers 111 and 113 may beformed of SiO₂, and the sealing spacer 128 may be formed of SiCO. SiCOmay be more etch resistant than SiO₂. The carbon content of SiCO may beless than the content of silicon and the content of oxygen. For example,SiCO may have a composition ratio of silicon (Si) 34 at %, oxygen 40 at%, and carbon 17 at %. SiCO may have a lower dielectric constant thansilicon nitride (Si₃N₄).

The sealing spacer 128 may be formed to have a thickness ofapproximately 50 Å to 100 Å. For example, a protrusion 128P of thesealing spacer 128 may have a thickness in a range from 50 Å to 100 Å inthe horizontal direction with respect to the orientation of FIG. 1. Thehigh wet-etch resistance of SiCO may reduce the thickness of the sealingspacer 128. Specifically, the high wet-etch resistance of SiCO mayprevent the sealing spacer 128 from being significantly etched when oneor more cleaning processes are performed. Thus, even when the sealingspacer 128 is formed to have a relatively small thickness and one ormore cleaning process are performed on the sealing spacer 128, thethickness of the sealing spacer 128 may remain sufficiently thick tosubstantially prevent Grown Bad Blocks (GBB) defects. As a result, thesize of the source contact plug 132 for separating cell blocks may bereduced, which eventually reduces the chip size. In addition, even whena vertical contact recess in which the source contact plug 132 is formedhas a relatively small size (e.g., a width in the horizontal directionof FIG. 1), because the sealing spacer 128 may formed to have arelatively small thickness, the vertical contact recess may be filledwith the source contact plug 132 without voids.

According to another embodiment of the present disclosure, the sealingspacer 128 may include SiCN, SiBCN, SiBN, or a combination thereof. Thewet-etch resistance of the sealing spacer 128 may be obtained by carbon,nitrogen, boron, or a combination thereof.

According to another embodiment of the present disclosure, the sealingspacer 128 may include a stack of one or more carbon-free silicon oxidelayers and one or more carbon-containing silicon oxide layers. Forexample, after a carbon-free silicon oxide layer (e.g., SiO₂ layer) isthinly deposited, a carbon-containing silicon oxide layer (e.g., SiCOlayer) may be deposited over the carbon-free silicon oxide layer. As aresult, the carbon-containing silicon oxide layer may be in directcontact with the source contact plug 132.

FIGS. 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14 are cross-sectionalviews illustrating a method for fabricating a vertical semiconductordevice in accordance with an embodiment of the present disclosure. Forexample, FIGS. 2 to 14 show a method for fabricating the verticalsemiconductor device 100 of FIG. 1.

Referring to FIG. 2, a first multi-layer stack 110S may be formed overthe lower structure 101. A second multi-layer stack 120M may be formedover the first multi-layer stack 110S.

The first multi-layer stack 110S may be a stack including a lower sourcelayer 102, a first liner layer 103, a source sacrificial layer 104, asecond liner layer 105, and an upper source layer 106. According to theembodiment shown in FIG. 2, the first multi-layer stack 110S may havethe source sacrificial layer 104 formed between the lower source layer103 and the upper source layer 106, the first liner layer 103 formedbetween the source sacrificial layer 104 and the lower source layer 102,and the second liner layer 105 formed between the source sacrificiallayer 104 and the upper source layer 106. The lower source layer 102,the upper source layer 106, and the source sacrificial layer 104 mayinclude the same material, and the first and second liner layers 103 and105 may include a material that is different from the materials of thelower source layer 102, the upper source layer 106, and the sourcesacrificial layer 104.

The lower source layer 102 and the upper source layer 106 may have anetch selectivity with respect to the first and second liner layers 103and 105. The lower source layer 102, the upper source layer 106, and thesource sacrificial layer 104 may include a semiconductor material, andthe first and second liner layers 103 and 105 may include a dielectricmaterial. The lower source layer 102, the upper source layer 106, andthe source sacrificial layer 104 may include polysilicon, and the firstand second liner layers 103 and 105 may include silicon oxide. The firstand second liner layers 103 and 105 may be thinner than the lower sourcelayer 102, the upper source layer 106, and the source sacrificial layer104. For example, the lower source layer 102 and the upper source layer106 may each have a thickness of approximately 150 nm in the verticaldirection of FIG. 2, and the first and second liner layers 103 and 105may each have a thickness of approximately 8 nm in the verticaldirection. The thickness of the source sacrificial layer 104 may be thesame as or thinner than the lower source layer 102 and the upper sourcelayer 106.

The first and second liner layers 103 and 105 may protect the lowersource layer 102 and the upper source layer 106 while the sourcesacrificial layer 104 is removed.

The first and second liner layers 103 and 105 may include a siliconoxide-based material. One or both of the first liner layer 103 and thesecond liner layer 105 may include SiO₂, SiCO, or a combination thereof.

The second multi-layer stack 120M may be thicker than the firstmulti-layer stack 110S. The second multi-layer stack 120M may include adielectric layer 111 and a sacrificial layer 112. The second multi-layerstack 120M may include an alternating stack of the dielectric layer 111and the sacrificial layer 112. The dielectric layer 111 and thesacrificial layer 112 may be alternately stacked several times. Thedielectric layer 111 and the sacrificial layer 112 may include differentmaterials. The dielectric layer 111 may have an etch selectivity withrespect to the sacrificial layer 112. The dielectric layer 111 mayinclude silicon oxide, and the sacrificial layer 112 may include siliconnitride. The dielectric layer 111 and the sacrificial layer 112 may havesubstantially the same thickness. The dielectric layer 111 and thesacrificial layer 112 may be thicker than the first and second linerlayers 103 and 105, and the dielectric layer 111 and the sacrificiallayer 112 may be thinner than the lower source layer 102 and the uppersource layer 106.

The dielectric layer 111 and the sacrificial layer 112 may be formedusing Chemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD).An uppermost dielectric layer (or a top dielectric layer) 113 formed ata top portion of the second multi-layer stack 120M may be attacked anddamaged by the subsequent processes. Therefore, the top dielectric layer113 may be formed thicker than the other dielectric layers 111 below thetop dielectric layer 113. The top dielectric layer 113 may be used as anetch barrier.

The first and second liner layers 103 and 105 may be thinner than thedielectric layers 111 and 113, the lower source layer 102, the uppersource layer 106, and the source sacrificial layer 104. The first andsecond liner layers 103 and 105 may include a material that is differentfrom those of the dielectric layers 111 and 113. The first and secondliner layers 103 and 105 may include a material having a high wet-etchresistance. The wet-etch resistance of the first and second liner layers103 and 105 may be obtained from carbon. The first and second linerlayers 103 and 105 may include a carbon-containing material, and thedielectric layers 111 and 113 may include a carbon-free material. Thedielectric layers 111 and 113 may include carbon-free silicon oxide, andthe first and second liner layers 103 and 105 may includecarbon-containing silicon oxide. For example, the dielectric layers 111and 113 may be SiO₂, and the first and second liner layers 103 and 105may be SiCO. SiCO may be more etch-resistant than SiO₂. The carboncontent of SiCO may be less than the silicon content and the oxygencontent. For example, SiCO may have a composition ratio of silicon (Si)34 at %, oxygen 40 at %, and carbon 17 at %.

The first and second liner layers 103 and 105 may be formed to have athickness of approximately 50 Å to 100 Å. For example, each of the firstand second liner layers 103 and 105 may have a thickness in a range from50 Å to 100 Å in the vertical direction with respect to the orientationof FIG. 2. The high wet-etch resistance of SiCO may reduce the thicknessof the first and second liner layers 103 and 105. For example, the highwet-etch resistance of SiCO may prevent the first and second linerlayers 103 and 105 from being significantly etched while the sourcesacrificial layer 104 is removed in a wet-etch process. Thus, even wheneach of the first and second liner layers 103 and 105 is formed to havea relatively small thickness, the first and second liner layers 103 and105 may protect the lower source layer 102 and the upper source layer106, respectively, while the source sacrificial layer 104 is removed inthe wet-etch process. As a result, the height of the first multi-layerstack 110S including the first and second liner layers 103 and 105 maybe reduced.

According to another embodiment of the present disclosure, the first andsecond liner layers 103 and 105 may include nitrogen, boron, or acombination thereof in addition to carbon.

According to another embodiment of the present disclosure, the first andsecond liner layers 103 and 105 may include a stack of one or morecarbon-free silicon oxide layers and one or more carbon-containingsilicon oxide layers. For example, after a carbon-free silicon oxidelayer is thinly deposited, a carbon-containing silicon oxide layer maybe deposited over the carbon-free silicon oxide layer.

According to another embodiment of the present disclosure, the firstliner layer 103 may be formed of SiO₂, and the second liner layer 105may be formed of SiCO.

According to another embodiment of the present disclosure, the stack ofthe second liner layer 105 and the upper source layer 106 may bereplaced with one layer of SiCO.

As described above, when one or both of the first liner layer 103 andthe second liner layer 105 is formed of SiCO and when the stack of thesecond liner layer 105 and the upper source layer 106 is replaced by onelayer of SiCO, not only there is no significant loss of thickness by awet-etch chemical, but also breakdown voltage (BV) characteristics withthe source contact plug may be improved due to a small loss in thethickness of SiCO while a subsequent process of forming horizontalcontact recesses and a process of expanding the horizontal contactrecesses (i.e., a dry etch process and a wet-etch process for removing ablocking layer, a charge trapping layer, and a tunnel dielectric layer)are performed.

Referring to FIG. 3, a vertical opening 114 may be formed. The verticalopening 114 may be formed by etching the second multi-layer stack 120Mand partially etching the first multi-layer stack 110S sequentially.

The vertical opening 114 may be formed substantially perpendicular tothe surface (e.g., a top surface) of the lower structure 101. Thevertical opening 114 may be shaped to penetrate through the secondmulti-layer stack 120M and to partially penetrate through the firstmulti-layer stack 110S. Although not shown, from the perspective of aplan view, a plurality of vertical openings 114 may be formed in a holearray structure. When the vertical openings 114 are formed, the surfaceof the lower structure 101 may not be exposed. For example, a portion ofthe lower source layer 102 may remain below the bottom surface of thevertical opening 114. The vertical opening 114 may be referred to as avertical recess, a through hole, a vertical hole, or a channel hole.

Referring to FIG. 4, a memory stack structure 120P may be formed in avertical opening 114. The memory stack structure 120P may have a pillarshape filling the vertical opening 114.

The memory stack structure 120P may include a blocking layer 115, acharge trapping layer 116, a tunnel dielectric layer 117, and a channellayer 118. The memory stack structure 120P may include an ONOPstructure. The ONOP structure may include a stack of an oxide layer, anitride layer, an oxide layer, and a polysilicon layer. The blockinglayer 115 and the tunnel dielectric layer 117 may include an oxide, andthe charge trapping layer 116 may include a nitride, and the channellayer 118 may include a polysilicon layer. According to an embodiment ofthe present disclosure, the blocking layer 115 may include a highdielectric material, and the high dielectric material may includealuminum oxide or hafnium oxide.

The channel layer 118 may be a cylinder shape having an inner space. Thetunnel dielectric layer 117 may be formed on the outer wall of thechannel layer 118, and the charge trapping layer 116 may be formed onthe outer wall of the tunnel dielectric layer 117. The blocking layer115 may be formed on an outer wall of the charge trapping layer 116.

The memory stack structure 120P may further include a core dielectriclayer 119. The inner space of the channel layer 118 may be substantiallycompletely filled with the core dielectric layer 119. The coredielectric layer 119 may include silicon oxide or silicon nitride.Although not illustrated, a conductive pad coupled to an upper endportion of the channel layer 118 may be further formed after the coredielectric layer 119 is recessed.

The stack of the blocking layer 115, the charge trapping layer 116, andthe tunnel dielectric layer 117 may be referred to as a memory layer,and the charge trapping layer 116 may be referred to as a memorymaterial layer.

Referring to FIG. 5, a vertical contact recess 121 may be formed. Thevertical contact recess 121 may be formed to be spaced apart from thememory stack structure 120P. The vertical contact recess 121 may beformed by etching the second multi-layer stack 120M, and the verticalcontact recess 121 may extend downward to a portion of the firstmulti-layer stack 110S. The bottom portion of the vertical contactrecess 121 may penetrate through the upper source layer 106 and thesecond liner layer 105. The etch process for forming the verticalcontact recess 121 may stop on the upper surface of the sourcesacrificial layer 104. According to another embodiment of the presentdisclosure, the top surface of the source sacrificial layer 104 may bepartially recessed while the vertical contact recess 121 is formed. Thevertical contact recess 121 may be referred to as a slit or trench. Fromthe perspective of a top view, the vertical contact recess 121 may havea line shape extending in one direction. The vertical contact recess 121may have a high aspect ratio perpendicular to the surface of the lowerstructure 101.

Referring to FIG. 6, a sacrificial sealing layer 122 may be formed onthe sidewall of the vertical contact recess 121. The sacrificial sealinglayer 122 may be formed as a spacer on the sidewall of the verticalcontact recess 121. The sacrificial sealing layer 122 may be formed byconformally forming a sacrificial sealing material layer and thenperforming a cutting process on the sacrificial sealing material layer.

The sacrificial sealing material layer for forming the sacrificialsealing layer 122 may include an oxide, a nitride, or a combinationthereof. For example, the sacrificial sealing material layer for thesacrificial sealing layer 122 may include a first sealing layer, asecond sealing layer, and a third sealing layer. The first sealing layerand the third sealing layer may include the same material, and thesecond sealing layer may include a material that is different from thematerials of the first and third sealing layers. The second sealinglayer may have an etch selectivity with respect to the first and thirdsealing layers. The first sealing layer and the third sealing layer mayinclude an oxide, and the second sealing layer may include a nitride.Thus, the sacrificial sealing layer 122 may include a NON structure. TheNON structure may refer to a stack of a nitride, an oxide, and anitride. The sacrificial sealing material layer may cover the bottomsurface and sidewalls of the vertical contact recess 121.

The sacrificial sealing material layer may be cut, and as a result, thesacrificial sealing layer 122 may be formed. The cutting process of thesacrificial sealing material layer may include an etch process, and thesurface (e.g., the top surface) of the source sacrificial layer 104 maybe exposed by the cutting process. After the cutting process, thesacrificial sealing material layer may remain as a spacer-typesacrificial sealing layer 122 on the sidewall of the vertical contactrecess 121. The cutting process of the sacrificial sealing materiallayer may include an etch-back process.

Subsequently, the source sacrificial layer 104 may be selectivelyremoved through the vertical contact recess 121. As a result, thehorizontal contact recess 123 may be formed. The vertical contact recess121 and the horizontal contact recess 123 may be coupled to each other.The horizontal contact recess 123 may be formed between the first linerlayer 103 and the second liner layer 105 by removing the sourcesacrificial layer 104 through a dip-out process. The horizontal contactrecess 123 may be parallel to the surface of the lower structure 101.When the source sacrificial layer 104 is removed, the first and secondliner layers 103 and 105 may have etch selectivity with respect to thesource sacrificial layer 104, and thus remain without beingsignificantly etched. The horizontal contact recess 123 may be formed inthe first multi-layer stack 110S. When the source sacrificial layer 104is removed, the lower source layer 102 and the upper source layer 106may not be removed. A wet-etch process may be applied to remove thesource sacrificial layer 104. Since the source sacrificial layer 104includes a polysilicon layer, the wet-etch process may include achemical capable of etching the polysilicon layer.

A portion of the horizontal contact recess 123 may expose the lowersidewall of the memory stack structure 120P. The outer wall of thememory stack structure 120P may be a blocking layer 115, and theblocking layer 115 of the memory stack structure 120P may be exposed bythe horizontal contact recess 123. Since the blocking layer 115 includesan oxide, the blocking layer 115 of the memory stack structure 120P mayhave etch selectivity with respect to the source sacrificial layer 104and may not be etched while the source sacrificial layer 104 is removed.From the perspective of a top view, the horizontal contact recess 123may have an annular shape surrounding the lower sidewall of the memorystack structure 120P. The horizontal contact recess 123 may be referredto as a source-level air gap.

Subsequently, the first and second liner layers 103 and 105 may beremoved. As a result, the height of the horizontal contact recess 123may increase in the vertical direction with respect to the orientationof FIG. 6. The horizontal contact recess 123 having the extended heightmay directly contact the lower source layer 102 and the upper sourcelayer 106.

While the first and second liner layers 103 and 105 are removed, theblocking layer 115 of the memory stack structure 120P may be removed.Thus, the charge trapping layer 116 of the memory stack structure 120Pmay be exposed. A wet-etch process may be applied to remove the firstand second liner layers 103 and 105. The wet-etch process may include achemical that may selectively remove silicon oxide.

Subsequently, the charge trapping layer 116 of the memory stackstructure 120P may be removed through the vertical contact recess 121and the horizontal contact recess 123. The charge trapping layer 116 maybe removed by a wet-etch process. When the charge trapping layer 116includes a nitride, the wet-etch process may include a chemical capableof etching the nitride.

By removing the charge trapping layer 116, the horizontal length of thehorizontal contact recess 123 may be increased.

Subsequently, the tunnel dielectric layer 117 of the memory stackstructure 120P may be removed through the vertical contact recess 121and the horizontal contact recess 123. The tunnel dielectric layer 117may be removed by a wet-etch process. When the tunnel dielectric layer117 includes an oxide, the wet-etch process may include a chemicalcapable of etching the oxide.

By removing the tunnel dielectric layer 117, the horizontal length ofthe horizontal contact recess 123 may be increased.

As described above, when the process of removing the source sacrificiallayer 104, the process of removing the first and second liner layers 103and 105, the process of removing the blocking layer 115, the process ofremoving the charge trapping layer 116, the process of removing thetunnel dielectric layer 117 are performed, the sacrificial sealing layer122 may serve as an etch barrier that protects the dielectric layers 111and 113 and the sacrificial layer 112.

A lower outer wall of the channel layer 118 of the memory stackstructure 120P may be exposed by the process of expanding the horizontalcontact recess 123. For example, an annular air gap may expose the lowerouter wall of the channel layer 118. The annular air gap may refer toportions from which the blocking layer 115, the charge trapping layer116, and the tunnel dielectric layer 117 are removed.

The first multi-layer stack in which one or more horizontal contactrecesses 123 are formed may be denoted by 110S′.

By the series of the processes illustrated in FIGS. 2 to 6, a contactopening penetrating through the first multi-layer stack 110S′ and thesecond multi-layer stack 120M may be formed. The contact opening mayinclude a vertical contact recess 121 and a horizontal contact recess123. The horizontal contact recess 123 may extend from the verticalcontact recess 121. The vertical contact recess 121 may extend in adirection (e.g., a vertical direction) perpendicular to the surface(e.g., the top surface) of the lower structure 101, and the horizontalcontact recess 123 may extend in a direction (e.g., a horizontaldirection) parallel to the surface of the lower structure 101. Thehorizontal contact recess 123 may have a high aspect ratio that isparallel to the surface of the lower structure 101. For example, thehorizontal contact recess 123 may have a relatively high ratio of thewidth in the horizontal direction over the height in the verticaldirection. The vertical contact recess 121 may have a high aspect ratioperpendicular to the lower structure 101. For example, the verticalcontact recess 121 may have a relatively high ratio of the height in thevertical direction over the width in the horizontal direction.

Referring to FIG. 7, a source contact material 124A may be formed tofill a contact opening, for example, the vertical recess 121 and thehorizontal contact recess 123. The source contact material 124A mayinclude a conductive material. The source contact material 124A mayinclude polysilicon. The source contact material 124A may includepolysilicon which is doped with phosphorus (P). The source contactmaterial 124A may include polysilicon containing carbon. The sourcecontact material 124A may include a stack of phosphorus-dopedpolysilicon (SiP) and carbon-doped polysilicon (SiC).

Subsequently, the source contact material 124A may be selectivelyremoved. The process of selectively removing the source contact material124A may include a recessing process, and the recessing process mayinclude a wet-etch process. The source contact layer 124 may be formedin the horizontal contact recess 123 by performing the wet-etchingprocess on the source contact material 124A. The source contact layer124 may fill the horizontal contact recess 123. For example, the sourcecontact material 124A may be etched using the sidewalls of thesacrificial sealing layer 122 to make the source contact layer 124self-aligned with the sidewalls of the sacrificial sealing layer 122. Asa result, the bottom surface of the vertical recess 121 may directlycontact the lower source layer 102. The source contact layer 124 mayremain in the horizontal contact recess 123, and the source contactlayer 124 may not remain in the vertical recess 121.

Although not illustrated, the source contact layer 124 may be exposed toan oxidation process subsequently. The oxidation process may include adry oxidation process or a wet oxidation process. An edge of the sourcecontact layer 124 may be oxidized by an oxidation process. As a result,a barrier oxide (not shown) may be formed at the edge of the sourcecontact layer 124 (that is, the portion exposed by the bottom portion ofthe vertical contact recess 121). The barrier oxide may include siliconoxide. The barrier oxide may protect the source contact layer 124 frombeing attacked during the subsequent process.

The first multi-layer stack 110S′ in which the source contact layer 124is formed may be simply referred to as a source-level stack 110. Thesource-level stack 110 may be disposed below the second multi-layerstack 120M, and the source contact layer 124 may be directly coupled tothe channel layer 118 of the memory stack structure 120P.

As described above, the source-level stack 110 which is formed by aseries of the processes of replacing the source sacrificial layer 104with the source contact layer 124 may have a structure in which thesource contact layer 124 is embedded.

Referring to FIGS. 8 to 10, the sacrificial layers 112 may be replacedwith the gate electrodes 127.

As shown in FIG. 8, the sacrificial layers 112 of the second multi-layerstack 120M may be selectively removed. As a result, the horizontal gaterecesses 125 may be formed between the dielectric layers 111. Since thesacrificial layer 112 includes a nitride, the sacrificial layer 112 maybe removed by a chemical including a phosphoric acid (H₃PO₄). While thesacrificial layer 112 is removed, the sacrificial sealing layer 122 mayalso be removed at the same time. According to another embodiment of thepresent disclosure, the sacrificial sealing layer 122 may be removedafter the sacrificial layer 112 is removed.

While the sacrificial layer 112 is removed, the source contact layer 124may be sufficiently protected by a barrier oxide. The barrier oxide mayserve as a protective layer for protecting the source contact layer 124from being attacked.

The horizontal gate recesses 125 may be continuous from the verticalcontact recess 121. Portions of the blocking layer 115 of the memorystack structure 120P may be exposed by the horizontal gate recesses 125.

After the horizontal gate recesses 125 are formed in the secondmulti-layer stack 120M in FIG. 7, a first intermediate multi-layer stack120′ may be formed. The first intermediate multi-layer stack 120′ mayhave a structure in which the dielectric layers 111 and the horizontalgate recesses 125 alternate. A horizontal gate recess 125 may also beformed between the top dielectric layer 113 and a neighboring dielectriclayer 111.

Referring to FIGS. 9 and 10, the gate electrodes 127 may fill thehorizontal gate recesses 125, respectively. The gate electrode 127 maybe formed by forming a gate material layer 126 to fill the horizontalgate recesses 125 (see FIG. 9). After the gate material layer 126 isformed, a second intermediate multi-layer stack 120″ may be formed. Thesecond intermediate multi-layer stack 120″ may have a structure in whichthe dielectric layers 111 and the gate material 126 alternate. The gatematerial 126 may cover the sidewall of the vertical contact recess 121.

Subsequently, as illustrated in FIG. 10, gate electrodes 127 may beformed by performing an etch-back process on the gate material layer126. The gate electrodes 127 may include a low-resistance material. Thegate electrodes 127 may include a metal-based material. The gateelectrodes 127 may include a metal, a metal silicide, a metal nitride,or a combination thereof. For example, the metal may include nickel,cobalt, platinum, titanium, tantalum, or tungsten. The metal silicidemay include nickel silicide, cobalt silicide, platinum silicide,titanium silicide, tantalum silicide, or tungsten silicide. The gateelectrodes 127 may include a stack of titanium nitride and tungsten.

The ends 127R of the gate electrodes 127 may have a shape that ishorizontally recessed from the ends of the dielectric layers 111. Theends 127R of the gate electrodes 127 may be exposed by the verticalcontact recess 121. The gate electrodes 127 may not contact the uppersource layer 106, the lower source layer 102, and the source contactlayer 124.

After the gate electrodes 127 are formed, an alternating stack 120 maybe formed. The alternating stack 120 may have a structure in which thedielectric layers 111 and the gate electrodes 127 are alternatelystacked. The memory stack structure 120P may penetrate through thealternating stack 120, and the vertical contact recess 121 may penetratethrough the alternating stack 120.

Referring to FIG. 11, the surface of the vertical contact recess 121 maybe sealed. The surface of the vertical contact recess 121 may be sealedby the sealing layer 128S. The sealing layer 128S may include one ormore protrusions 128P, and the protrusions 128P may seal the ends 127Rof the gate electrodes 127. The sealing layer 128S may seal the sidesurfaces of the dielectric layers 111 and 113. The sealing layer 128Smay seal the side surface of the source contact layer 124. The sealinglayer 128S may seal the side surface of the upper source layer 106 andmay seal the exposed surface of the lower source layer 102. The sealinglayer 128S may include a silicon oxide-based material. The sealing layer128S may include a low-dielectric material. The low-dielectric materialmay have a lower dielectric constant than silicon nitride. The materialof the sealing layer 128S may have a dielectric constant lower thanapproximately 7.

The sealing layer 128S may be thinner than the dielectric layers 111 and113 and the gate electrode 127. The sealing layer 128S may be a layer ofa material that is different from that of the dielectric layers 111 and113. The sealing layer 128S may be a layer of a material that isdifferent from that of the gate electrode 127. The sealing layer 128Smay include a material having high wet-etch resistance. The wet-etchresistance of the sealing layer 128S may be obtained by carbon. Thesealing layer 128S may be formed of a carbon-containing material, andthe dielectric layers 111 and 113 may be formed of a carbon-freematerial. The dielectric layers 111 and 113 may be formed of carbon-freesilicon oxide, and the sealing layer 128S may be formed ofcarbon-containing silicon oxide. For example, the dielectric layers 111and 113 may be formed of SiO₂, and the sealing layer 128S may be formedof SiCO. SiCO may be more etch-resistant than SiO₂. The carbon contentin SiCO may be less than the silicon content and the oxygen content. Forexample, SiCO may have a composition ratio of silicon (Si) 34 at %,oxygen 40 at %, and carbon 17 at %. SiCO may have a lower dielectricconstant than silicon nitride (Si₃N₄).

The sealing layer 128S may be formed to a thickness of approximately 50Å to 100 Å. The high wet-etch resistance of SiCO may reduce thethickness of the sealing layer 128S. As a result, the size of thevertical contact recess 121 for separating cell blocks may be reduced,which may reduce the chip size. In a comparative example, when a sealinglayer is formed of SiO₂, the sealing layer should be formed to have athickness of approximately 150 Å or more in consideration of loss in thesubsequent processes (e.g., a cleaning process), and the thick SiO₂ mayinhibit a vertical contact recess from being filled with a sourcecontact plug without voids. In order to improve the gapfillcharacteristics of the source contact plug, the vertical contact recessin the comparative example should be formed to have a relatively largesize. In contrast, since SiCO of the sealing layer 128S in theembodiment of the present disclosure has greater wet-etch resistancethan SiO₂, the sealing layer 128S of SiCO may be formed thinner than thesealing layer of SiO₂ in the comparative example. Therefore, even thoughthe size of the vertical contact recess 121 is small, a source contactplug may fill the vertical contact recess 121 without voids.

According to another embodiment of the present disclosure, the sealinglayer 128S may include a material that is wet-etch resistant to thesubsequent processes. The sealing layer 128S may include SiCN, SiBCN,SiBN, or a combination thereof. The wet-etch resistance of the sealinglayer 128S may be obtained from carbon, nitrogen, boron, or acombination thereof.

According to another embodiment of the present disclosure, a seed layermay be formed prior to the formation of the sealing layer 128S. The seedlayer may form a thin silicon oxide or silicon nitride. By forming theseed layer, the conformality of the sealing layer 128S may be improved.

According to another embodiment of the present disclosure, the sealinglayer 128S may include a stack of one or more carbon-free silicon oxidelayers and one or more carbon-containing silicon oxide layers. Forexample, after a carbon-free silicon oxide layer is thinly deposited, acarbon-containing silicon oxide layer may be deposited over thecarbon-free silicon oxide layer. The carbon-free silicon oxide mayimprove the conformality of the carbon-containing silicon oxide as theseed layer.

Although not illustrated, the sealing layer 128S may seal the uppersurface of the top dielectric layer 113.

Referring to FIG. 12, the sealing layer 128S may be selectively removedto expose the surface of the lower source layer 102. As a result, asealing spacer 128 may be formed on the sidewall of the vertical contactrecess 121. The bottom portion of the sealing spacer 128 maysubstantially completely cover the side of the source contact layer 124and the side of the upper source layer 106. The sealing spacer 128 mayinclude one or more protrusions 128P, and the protrusions 128P may sealthe ends 127R of the gate electrodes 127. The sealing spacer 128 mayseal the sides of the dielectric layers 111 and 113.

The sealing spacer 128 may be vertically continuous along the stackingdirection of the dielectric layers 111 and 113 and the gate electrodes127. From the perspective of a top view, the sealing spacer 128 may be aclosed loop-shape sealing the sidewall of the vertical contact recess121.

Since the thickness of the sealing layer 128S is thin, the open area ofthe bottom surface of the vertical contact recess 121 may be increasedin an etch process for forming the sealing spacer 128. As a result, itis possible to secure an electrically low resistance and processstability.

After the sealing spacer 128 is formed, a post-cleaning process may beperformed.

Referring to FIGS. 13 and 14, the vertical contact recess 121 may befilled with a contact material. For example, a source contact plug 132may be formed in the vertical contact recess 121. The source contactplug 132 may fill the vertical contact recess 121. The source contactplug 132 may include a stack of a silicon-containing material 129 and ametal-containing material 131, and may further include a barriermaterial 130 between the silicon-containing material 129 and themetal-containing material 131. The silicon-containing material 129 mayinclude polysilicon, and the metal-containing material 131 may includetungsten. The barrier material 130 may include titanium nitride.According to another embodiment of the present disclosure, the sourcecontact plug 132 may be formed of tungsten alone.

The silicon-containing material 129 may be formed by depositingpolysilicon to fill the vertical contact recess 121 and performing anetch-back process onto the polysilicon. A pre-cleaning process may beperformed before the deposition of polysilicon, and a post-cleaningprocess may be performed after the etch-back process of the polysilicon.The silicon-containing material 129 may be in contact with the sealingspacer 128.

After the silicon-containing material 129 is formed, the barriermaterial 130 may be conformally deposited. A pre-cleaning process may beperformed before the deposition of the barrier material 130. After thebarrier material 130 is conformally deposited, the remainder of thevertical contact recess 121 may be filled with the metal-containingmaterial 131. After the barrier material 130 and the metal-containingmaterial 131 are sequentially deposited, a planarization process usingChemical Mechanical Polishing (CMP) may be performed. As a result, thebarrier material 130 and the metal-containing material 131 may remainonly in the vertical contact recess 121. The barrier material 130 may bein direct contact with the sealing spacer 128, and the metal-containingmaterial 131 may not contact the sealing spacer 128.

Although a plurality of cleaning processes are performed during theprocess of forming the sealing spacer 128, the process of forming thesilicon-containing material 129, and the process of depositing thebarrier material 130, the thickness loss of the sealing spacer 128 mayhardly occur.

As described above, the source-level stack 110 and the alternating stack120 may be formed over the lower structure 101. The source-level stack110 may include the lower source layer 102, the source contact layer124, and the upper source layer 106. The alternating stack 120 may beformed by alternately stacking the dielectric layers 111 and the gateelectrodes 127. The memory stack structure 120P may penetrate throughthe alternating stack 120 and the source-level stack 110. The lowerouter wall of the channel layer 118 of the memory stack structure 120Pmay directly contact the source contact layer 124. The channel layer118, the lower source layer 102, the upper source layer 106, and thesource contact plug 132 may be electrically connected through the sourcecontact layer 124.

The gate electrodes 127 and the source contact plug 132 may beelectrically disconnected from each other by the sealing spacer 128. Thegate electrodes 127 and the source contact plug 132 may be physicallydisconnected by the sealing spacer 128. A high voltage may be repeatedlyapplied between the gate electrode 127 and the source contact plug 132,thereby increasing Grown Bad Blocks (GBB). The GBB is a phenomenon thatas the number of operations is increased, the number of bad blocks maybe increased. According to the embodiment of the present disclosure, thesealing spacer 128 may include the carbon-containing material, therebypreventing GBB defects. In other words, since the sealing spacer 128 isformed of a material having a high wet-etch resistance, the thicknessloss of the sealing spacer 128 may not substantially occur during thesubsequent cleaning processes, and thus the sealing spacer 128 may besecured with a thickness that is thick enough to withstand the highvoltage applied between the gate electrode 127 and the source contactplug 132.

Also, since the sealing spacer 128 is formed of a low dielectricmaterial according to the embodiment of the present disclosure, theparasitic capacitance between the gate electrodes 127 and the sourcecontact plug 132 may be relatively small.

Referring to FIGS. 2 to 14, a method for fabricating a verticalsemiconductor device may include: forming the first multi-layer stack110S that includes the sacrificial source layer 104 over the lowerstructure 101; forming the second multi-layer stack 120M in which thedielectric layers 111 and the sacrificial layers 112 are alternatelystacked over the first multi-layer stack 110S; forming the memory stackstructure 120P that includes the channel layer 118 extending through thesecond multi-layer stack 120M and the first multi-layer stack 110S;forming the vertical contact recess 121 to be spaced apart from thememory stack structure 120P and to extend through the second multi-layerstack 120M and the first multi-layer stack 110S; forming the horizontalcontact recess 123 by selectively removing the sacrificial source layer104 through the vertical contact recess 121; expanding the horizontalcontact recess 123 to expose the lower outer wall of the channel layer118; filling the expanded horizontal contact recess 123 with the sourcecontact layer 124; replacing the sacrificial layers 112 with the gateelectrodes 127; forming the sealing spacer 128 that seals the sidewallof the vertical contact recess 121 over the source contact layer 124 andthe gate electrodes 127; and forming the source contact plug 132 in thevertical contact recess 121. The sealing spacer 128 may be formed ofcarbon-containing silicon oxide.

FIG. 15 is a cross-sectional view illustrating a vertical semiconductordevice 200 in accordance with another embodiment of the presentdisclosure.

Referring to FIG. 15, the vertical semiconductor device 200 may bepositioned over the lower structure 101, and the vertical semiconductordevice 200 may include an alternating stack 120 in which gate electrodes127 and dielectric layers 111 are alternately stacked, a memory stackstructure 120P including a channel layer 118 extending to penetratethrough the alternating stack 120 and a stack of layers (or a memorylayer) 115, 116, and 117 surrounding the channel layer 118, a sourcecontact layer 124 disposed between the lower structure 101 and thealternating stack 120 to contact the lower outer wall of the channellayer 118, and a source contact plug 132 extending through thealternating stack 120 to be spaced apart from the memory stack structure120P, and a sealing spacer 128 having an etch resistance that isdifferent from the etch resistance of the dielectric layers 111 whilesealing the outer wall of the source contact plug. The sealing spacer128 may seal the gate electrodes 127 and be disposed between the sourcecontact plug 132 and the gate electrodes 127, and may have an etchresistance that is different from that of the dielectric layers 111. Theouter wall of the source contact plug 132 may be surrounded by thesealing spacer 128, which may vertically extend to cover the gateelectrodes 127, the dielectric layers 111, a carbon-containing linerlayer 105′, and the source contact layer 124.

The lower structure 101 may include a material suitable forsemiconductor processing. The lower structure 101 may include asubstrate, and the substrate may include a semiconductor substrate. Forexample, the lower structure 101 may include a silicon substrate, amonocrystalline silicon substrate, a polysilicon substrate, an amorphoussilicon substrate, a silicon germanium substrate, a monocrystallinesilicon germanium substrate, a polycrystalline silicon germaniumsubstrate, a carbon-doped silicon substrate, a combination thereof, or amultilayer thereof. The lower structure 101 may include othersemiconductor materials, such as germanium. The lower structure 101 mayinclude a III/V-group semiconductor substrate, such as a compoundsemiconductor substrate, e.g., GaAs. The lower structure 101 may includea silicon on insulator (SOI) substrate. Although not shown, according toanother embodiment of the present disclosure, the lower structure 101may include a substrate, at least one or more control circuits formedover the substrate, and a multi-layer metal line.

A multi-layer stack structure may be disposed over the lower structure101 and include a source-level stack 110 and an alternating stack 120over the source-level stack 110. The source-level stack 110 may have alower height than the alternating stack 120.

The source-level stack 110 may include a lower source layer 102, asource contact layer 124, and a carbon-containing liner layer 105′. Thesource contact layer 124 may be formed over the lower source layer 102,and the carbon-containing liner layer 105′ may be formed over the sourcecontact layer 124. The source contact layer 124 may be disposed betweenthe lower source layer 102 and the carbon-containing liner layer 105′.The lower source layer 102 and the source contact layer 124 may includea semiconductor material. The lower source layer 102 and the sourcecontact layer 124 may include polysilicon. The source contact layer 124may include polysilicon doped with phosphorus (P). The source contactlayer 124 may include carbon-containing polysilicon. The source contactlayer 124 may include a stack of phosphorus-doped polysilicon (SiP) andcarbon-doped polysilicon (SiC). The lower source layer 102 may includeundoped polysilicon or doped polysilicon.

The carbon-containing liner layer 105′ may include a silicon oxide-basedmaterial. The carbon-containing liner layer 105′ may include at leastSiCO.

The carbon-containing liner layer 105′ may be a layer of a material thatis different from those of the dielectric layers 111 and 113. Thecarbon-containing liner layer 105′ may include a material having a highwet-etch resistance. The wet-etch resistance of the carbon containingliner layer 105′ may be obtained from carbon. The carbon-containingliner layer 105′ may be a carbon-containing material, and the dielectriclayers 111 and 113 may be a carbon-free material. The dielectric layers111 and 113 may be carbon-free silicon oxide, and the carbon-containingliner layer 105′ may be carbon-containing silicon oxide. For example,the dielectric layers 111 and 113 may be SiO₂ and the carbon-containingliner layer 105′ may be SiCO. SiCO may be more etch-resistant than SiO₂.The carbon content in SiCO may be smaller than the silicon content andthe oxygen content. For example, SiCO may have a composition ratio ofsilicon (Si) 34 at %, oxygen 40 at %, and carbon 17 at %.

The carbon-containing liner layer 105′ may be formed to a thickness ofapproximately 50 Å to 100 Å. For example, the carbon-containing linerlayer 105′ may have a thickness in a range from 50 Å to 100 Å in thevertical direction with respect to the orientation of FIG. 15. The highwet-etch resistance of SiCO may reduce the thickness of thecarbon-containing liner layer 105′. As a result, the height of thesource-level stack 110 may be reduced. The bottom dielectric layer 111among the dielectric layers 111 may have a thickness that is thinnerthan each of the dielectric layers 111 at a higher level than the bottomdielectric layer 111. For example, when the carbon-containing linerlayer 105′ is formed of SiCO, the thickness of the bottom dielectriclayer 111 may be relatively thin (e.g., approximately 200 Å). As aresult, a dopant diffusion movement distance from the source contactlayer 124 to the channel layer 118 adjacent to the bottom gate electrode127 may be shortened. The dielectric layers 111 at a higher level thanthe bottom dielectric layer 111 may be approximately 300 Å thick.

According to another embodiment of the present disclosure, thecarbon-containing liner layer 105′ may be replaced with a materialcontaining nitrogen, boron, or a combination thereof in addition tocarbon.

The alternating stack 120 may be called a memory cell stack or a memorycell string. The alternating stack 120 may have a structure in which aplurality of dielectric layers 111 and a plurality of gate electrodes127 are alternately stacked. The uppermost dielectric layer 113 amongthe dielectric layers 111 may be thicker than the other dielectriclayers 111. The dielectric layers 111 may include silicon oxide. Thegate electrodes 127 may include a low-resistance material. The gateelectrodes 127 may include a metal-based material. The gate electrodes127 may include a metal, a metal silicide, a metal nitride, or acombination thereof. For example, the metal may include nickel, cobalt,platinum, titanium, tantalum, or tungsten. The metal silicide mayinclude nickel silicide, cobalt silicide, platinum silicide, titaniumsilicide, tantalum silicide or tungsten silicide. The gate electrodes127 may include a stack of titanium nitride and tungsten. The ends(e.g., ends 127R in FIG. 24) of the gate electrodes 127 may have a shapethat is horizontally recessed from the ends of the dielectric layers111.

The memory stack structure 120P may extend vertically to penetratethrough the alternating stack 120. The memory stack structure 120P mayhave a pillar shape. The memory stack structure 120P may include ablocking layer 115, a charge trapping layer 116, a tunnel dielectriclayer 117, a channel layer 118, and a core dielectric layer 119. Thememory stack structure 120P may include an ONOP structure. The ONOPstructure may include a stack of an oxide layer, a nitride layer, anoxide layer, and a polysilicon layer. The blocking layer 115 and thetunnel dielectric layer 117 may include an oxide, and the chargetrapping layer 116 may include a nitride, and the channel layer 118 mayinclude polysilicon. According to an embodiment of the presentdisclosure, the blocking layer 115 may include a high dielectricmaterial, and the high dielectric material may include aluminum oxide orhafnium oxide. The channel layer 118 may be a cylindrical shape havingan inner space. The tunnel dielectric layer 117 may be formed on theouter wall of the channel layer 118, and the charge trapping layer 116may be formed on the outer wall of the tunnel dielectric layer 117. Theblocking layer 115 may be formed on the outer wall of the chargetrapping layer 116. The inner space of the channel layer 118 may besubstantially completely filled with the core dielectric layer 119. Thecore dielectric layer 119 may include silicon oxide or silicon nitride.The stack of the blocking layer 115, the charge trapping layer 116, andthe tunnel dielectric layer 117 may be called a memory layer115/116/117.

The source contact plug 132 may include a stack of a silicon-containingmaterial 129 and a metal-containing material 131, and it may furtherinclude a barrier material 130 between the silicon-containing material129 and the metal-containing material 131. The silicon-containingmaterial 129 may include polysilicon, and the metal-containing material131 may include tungsten. The barrier material 130 may include titaniumnitride. According to another embodiment of the present disclosure, thesource contact plug 132 may be formed of tungsten alone. The lowerportion of the source contact plug 132 may be coupled to the lowersource layer 102 of the source-level stack 110.

The sealing spacer 128 may be formed between the source contact plug 132and the gate electrodes 127. The sealing spacer 128 may extend to beformed between the dielectric layers 111 and 113 and the source contactplug 132. The sealing spacer 128 may be continuous along the stackingdirection of the alternating stack 120. The sealing spacer 128 mayinclude one or more protrusions 128P, and the protrusions 128P may becoupled to the ends of the gate electrodes 127, respectively. Theprotrusions 128P of the sealing spacer 128 may seal the ends of the gateelectrodes 127. The sealing spacer 128 may seal the sides of thedielectric layers 111 and 113. The sealing spacer 128 may seal the sideof the source contact layer 124. The sealing spacer 128 may seal theside of the carbon-containing liner layer 105′ and may not seal aportion of the surface of the lower source layer 102. The sealing spacer128 may substantially fully surround the outer wall of the sourcecontact plug 132.

The sealing spacer 128 may include a silicon oxide-based material. Thesealing spacer 128 may include a low dielectric material. The lowdielectric material may have a lower dielectric constant than siliconnitride. The sealing spacer 128 may have a dielectric constant lowerthan approximately 7. The sealing spacer 128 may be thinner than thedielectric layers 111 and 113 and the gate electrodes 127. The sealingspacer 128 may be a layer of a material that is different from those ofthe dielectric layers 111 and 113. The sealing spacer 128 may be a layerof a material that is different from that of the gate electrodes 127.The carbon-containing liner layer 105′ and the sealing spacer 128 mayinclude the same material. The sealing spacer 128 may include a materialhaving a high wet-etch resistance. The wet-etch resistance of thesealing spacer 128 may be obtained from carbon. The sealing spacer 128may include a carbon-containing material, and the dielectric layers 111and 113 may include a carbon-free material. The dielectric layers 111and 113 may be formed of carbon-free silicon oxide, and the sealingspacer 128 may be formed of carbon-containing silicon oxide. Forexample, the dielectric layers 111 and 113 may be formed of SiO₂, andthe sealing spacer 128 may be formed of SiCO. SiCO may be moreetch-resistant than SiO₂. The carbon content of SiCO may be less thanthe silicon content and the oxygen content of SiCO. For example, SiCOmay have a composition ratio of silicon (Si) 34 at %, oxygen 40 at %,and carbon 17 at %. SiCO may have a lower dielectric constant thansilicon nitride (Si₃N₄).

The sealing spacer 128 may be formed to have a thickness ofapproximately 50 Å to 100 Å. The high wet-etch resistance of SiCO mayreduce the thickness of the sealing spacer 128. As a result, the size ofthe source contact plug 132 for separating cell blocks may be reduced,and thus the chip size may be reduced. The sealing spacer 128 may bethinner than the carbon-containing liner layer 105′.

According to another embodiment of the present disclosure, the sealingspacer 128 may include SiCN, SiBCN, SiBN, or a combination thereof. Thewet-etch resistance of the sealing spacer 128 may be obtained fromcarbon, nitrogen, boron, or a combination thereof.

According to another embodiment of the present disclosure, the sealingspacer 128 may include a stack of one or more carbon-free silicon oxidelayers and one or more carbon-containing silicon oxide layers. Forexample, after thinly depositing a carbon-free silicon oxide layer, acarbon-containing silicon oxide layer may be deposited over thecarbon-free silicon oxide layer.

FIGS. 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, and 28 arecross-sectional views illustrating a method for fabricating a verticalsemiconductor device in accordance with another embodiment of thepresent disclosure. For example, FIGS. 16 to 28 show a method forfabricating the vertical semiconductor device 200 of FIG. 5.

Referring to FIG. 16, a first multi-layer stack 110S may be formed overthe lower structure 101. The first multi-layer stack 110S may have astack structure including a lower source layer 102, a first liner layer103, a source sacrificial layer 104, and a second liner layer 105′. Inthe first multi-layer stack 110S according to the embodiment shown inFIG. 16, a first liner layer 103 may be formed between the lower sourcelayer 102 and the source sacrificial layer 104, and a second liner layer105′ may be formed over the source sacrificial layer 104. The lowersource layer 102 and the source sacrificial layer 104 may include thesame material, and the first and second liner layers 103 and 105′ mayinclude a material that is different from the materials of the lowersource layer 102 and the source sacrificial layer 104. The first andsecond liner layers 103 and 105′ may have an etch selectivity withrespect to the source sacrificial layer 104. The lower source layer 102and the source sacrificial layer 104 may include a semiconductormaterial, and the first and second liner layers 103 and 105′ may includea dielectric material. The lower source layer 102 and the sourcesacrificial layer 104 may include polysilicon, and the first and secondliner layers 103 and 105′ may include silicon oxide. The sourcesacrificial layer 104 may have the same thickness or thinner thicknessthan the lower source layer 102 and the second liner layer 105′. Thesecond liner layer 105′ may be thicker than the first liner layer 103.

The first and second liner layers 103 and 105′ may protect the lowersource layer 102 while the source sacrificial layer 104 is removed.

The first and second liner layers 103 and 105′ may include a siliconoxide-based material. One or both of the first liner layer 103 and thesecond liner layer 105′ may include SiO₂, SiCO, or a combinationthereof.

The second liner layer 105′ may be a layer of a material that isdifferent from the material of the first liner layer 103. The secondliner layer 105′ may include a material having high wet-etch resistance.The wet-etch resistance of the second liner layer 105′ may be obtainedfrom carbon. The second liner layer 105′ may include a carbon-containingmaterial, and the first liner layer 103 may include a carbon-freematerial. The first liner layer 103 may be formed of a carbon-freesilicon oxide, and the second liner layer 105′ may be formed of acarbon-containing silicon oxide. For example, the first liner layer 103may be formed of SiO₂, and the second liner layer 105′ may be formed ofSiCO. SiCO may be more etch-resistant than SiO₂. The carbon content ofSiCO may be less than the silicon content and the oxygen content ofSiCO. For example, SiCO may have a composition ratio of silicon (Si) 34at %, oxygen 40 at %, and carbon 17 at %.

The first and second liner layers 103 and 105′ may be formed to have athickness of approximately 50 Å to 100 Å. The high wet-etch resistanceof SiCO may reduce the thickness of the second liner layer 105′. As aresult, the height of the first multi-layer stack 110S may be reduced.

According to another embodiment of the present disclosure, the secondliner layer 105′ may include nitrogen, boron, or a combination thereofin addition to carbon.

As described above, the first liner layer 103 may be formed of SiO₂, andthe second liner layer 105′ may be formed of SiCO. Unlike FIG. 2, inFIG. 16, the upper source layer 106 may be omitted, and only the secondliner layer 105′ may be formed. The second liner layer 105′ has asmaller thickness than a thickness of the upper source layer 106.

Subsequently, a second multi-layer stack 120M may be formed over thefirst multi-layer stack 110S. The second multi-layer stack 120M may bethicker than the first multi-layer stack 110S. The second multi-layerstack 120M may include a dielectric layer 111 and a sacrificial layer112. The second multi-layer stack 120M may include an alternating stackof the dielectric layer 111 and the sacrificial layer 112. Thedielectric layer 111 and the sacrificial layer 112 may be alternatelystacked several times. The dielectric layer 111 and the sacrificiallayer 112 may include different materials. The dielectric layer 111 mayhave an etch selectivity with respect to the sacrificial layer 112. Thedielectric layer 111 may include silicon oxide, and the sacrificiallayer 112 may include silicon nitride. The dielectric layer 111 and thesacrificial layer 112 may have substantially the same thickness.

The dielectric layer 111 and the sacrificial layer 112 may be formed byChemical Vapor Deposition (CVD) or Atomic Layer Deposition (ALD). Anuppermost dielectric layer (or a top dielectric layer) 113 formed at atop portion of the second multi-layer stack 120M may be attacked anddamaged by the subsequent processes. Therefore, the top dielectric layer113 may be formed thicker than that of the dielectric layers 111disposed under the top dielectric layer 113. The top dielectric layer113 may be used as an etch barrier. A lowermost dielectric layer (or abottom dielectric layer) 111 in contact with the second liner layer 105′among the dielectric layers 111 may be thinner than other dielectriclayers 111 over the bottom dielectric layer 111. For example, when thesecond liner layer 105′ is formed of SiCO, the thickness of thelowermost dielectric layer 111 may be formed thin (e.g., approximately200 Å). The other dielectric layers 111 over the bottom dielectric layer111 may have a thickness of approximately 300 Å.

Referring to FIG. 17, a vertical opening 114 may be formed. The verticalopening 114 may be formed by etching the second multi-layer stack 120Mand partially etch the first multi-layer stack 110S sequentially.

The vertical opening 114 may be formed substantially perpendicular tothe surface (e.g., a top surface) of the lower structure 101. Thevertical opening 114 may be shaped to penetrate though the secondmulti-layer stack 120M, or it may be shaped to partially penetratethough the first multi-layer stack 110S. Although not shown, from theperspective of a plan view, the vertical openings 114 may be formed inplural, and may have a hole array structure. When the vertical opening114 is formed, the surface of the lower structure 101 may not beexposed. For example, a portion of the lower source layer 102 may remainbelow the bottom of the vertical opening 114. The vertical opening 114may be called a vertical recess, a vertical hole, or a channel hole.

Referring to FIG. 18, a memory stack structure 120P may be formed in thevertical opening 114. The memory stack structure 120P may have a pillarshape that fills the vertical opening 114.

The memory stack structure 120P may include a blocking layer 115, acharge trapping layer 116, a tunnel dielectric layer 117, and a channellayer 118. The memory stack structure 120P may include an ONOPstructure. The ONOP structure may include a stack of an oxide layer, anitride layer, an oxide layer, and a polysilicon layer. The blockinglayer 115 and the tunnel dielectric layer 117 may include an oxide, thecharge trapping layer 116 may include a nitride, and the channel layer118 may include a polysilicon layer. According to an embodiment of thepresent disclosure, the blocking layer 115 may include a high dielectricmaterial, and the high dielectric material may include aluminum oxide orhafnium oxide.

The channel layer 118 may have a cylindrical shape having an innerspace. A tunnel dielectric layer 117 may be formed on the outer wall ofthe channel layer 118, and a charge trapping layer 116 may be formed onthe outer wall of the tunnel dielectric layer 117. The blocking layer115 may be formed on the outer wall of the charge trapping layer 116.

The memory stack structure 120P may further include a core dielectriclayer 119. The inner space of the channel layer 118 may be substantiallycompletely filled with the core dielectric layer 119. The coredielectric layer 119 may include silicon oxide or silicon nitride.Although not illustrated, a conductive pad coupled to the upper end ofthe channel layer 118 may be further formed after the core dielectriclayer 119 is recessed.

The stack of the blocking layer 115, the charge trapping layer 116, andthe tunnel dielectric layer 117 may be referred to as a memory layer,and the charge trapping layer 116 may be referred to as a memorymaterial layer.

Referring to FIG. 19, a vertical contact recess 121 may be formed. Thevertical contact recess 121 may be formed to be spaced apart from thememory stack structure 120P. The vertical contact recess 121 may beformed by etching the second multi-layer stack 120M, and the verticalcontact recess 121 may extend downward to a portion of the firstmulti-layer stack 110S. The bottom portion of the vertical contactrecess 121 may penetrate through the second liner layer 105′. The etchprocess for forming the vertical contact recess 121 may stop at thesource sacrificial layer 104. According to another embodiment of thepresent disclosure, the top surface of the source sacrificial layer 104may be partially recessed during the vertical contact recess 121 isformed. The vertical contact recess 121 may be referred to as a slit ortrench. From the perspective of a top view, the vertical contact recess121 may have a line shape extending in one direction. The verticalcontact recess 121 may have a high aspect ratio perpendicular to thesurface of the lower structure 101.

Referring to FIG. 20, a sacrificial sealing layer 122 may be formed onthe sidewall of the vertical contact recess 121. The sacrificial sealinglayer 122 may be formed as a spacer on the sidewall of the verticalcontact recess 121. The sacrificial sealing layer 122 may be formed byconformally forming a sacrificial sealing material layer and thenperforming a cut process on the sacrificial sealing material layer.

The sacrificial sealing material layer for forming the sacrificialsealing layer 122 may include an oxide, a nitride, or a combinationthereof. For example, the sacrificial sealing material layer, whichincludes a combination of an oxide and a nitride, may include a firstsealing layer, a second sealing layer, and a third sealing layer. Thefirst sealing layer and the third sealing layer may include the samematerial, and the second sealing layer may include a material that isdifferent from those of the first and third sealing layers. The secondsealing layer may have an etch selectivity with respect to the first andthird sealing layers. The first sealing layer and the third sealinglayer may include an oxide, and the second sealing layer may include anitride. Thus, the sacrificial sealing layer 122 may include a NONstructure. The NON structure may refer to a stack of a nitride, anoxide, and a nitride. The sacrificial sealing material layer may coverthe bottom and sidewalls of the vertical contact recess 121.

The sacrificial sealing material layer may go through a cutting process,and as a result, the sacrificial sealing layer 122 may be formed. Thecutting process of the sacrificial sealing material layer may include anetch process, and the surface (e.g., the top surface) of the sourcesacrificial layer 104 may be exposed as a result of the cutting process.After the cutting process, the sacrificial sealing material layer mayremain as a spacer-type sacrificial sealing layer 122 on the sidewall ofthe vertical contact recess 121. The cutting process of the sacrificialsealing material layer may include an etch-back process.

Subsequently, the source sacrificial layer 104 may be selectivelyremoved through the vertical contact recess 121. As a result, ahorizontal contact recess 123 may be formed. The vertical contact recess121 and the horizontal contact recess 123 may be coupled to each other.The horizontal contact recess 123 may be formed between the second linerlayer 105′ and the first liner layer 103 by removing the sourcesacrificial layer 104 by a dip-out process. The horizontal contactrecess 123 may be parallel to the surface of the lower structure 101.When the source sacrificial layer 104 is removed, the first and secondliner layers 103 and 105′ may remain without being removed due to theiretch selectivity. The horizontal contact recess 123 may be formed in thefirst multi-layer stack 110S. When the source sacrificial layer 104 isremoved, the lower source layer 102 may not be removed. A wet-etchprocess may be applied to remove the source sacrificial layer 104. Sincethe source sacrificial layer 104 includes a polysilicon layer, thewet-etch process may include a chemical capable of etching thepolysilicon layer.

A portion of the horizontal contact recess 123 may expose the lowersidewall of the memory stack structure 120P. The outer wall of thememory stack structure 120P may be a blocking layer 115, and theblocking layer 115 of the memory stack structure 120P may be exposed bythe horizontal contact recess 123. Since the blocking layer 115 includesan oxide, the blocking layer 115 of the memory stack structure 120P mayhave an etch selectivity with respect to the source sacrificial layer104 and thus it may not be etched while the source sacrificial layer 104is removed. From the perspective of a top view, the horizontal contactrecess 123 may be shaped to surround the outer wall of the bottomportion of the memory stack structure 120P.

Subsequently, the first liner layer 103 may be removed. As a result, theheight of the horizontal contact recess 123 may increase in the verticaldirection with respect to the orientation of FIG. 20. The expandedhorizontal contact recess 123 may directly contact the lower sourcelayer 102 and the second liner layer 105′.

While the first liner layer 103 is removed, the blocking layer 115 ofthe bottom portion of the memory stack structure 120P may be removed.Thus, the charge trapping layer 116 of the memory stack structure 120Pmay be exposed. A wet-etch process may be applied to remove the firstliner layer 103. The wet-etch process may include a chemical that mayselectively remove silicon oxide. While the first liner layer 103 isremoved, the second liner layer 105′ may not be removed because it has awet-etch resistance.

Subsequently, the charge trapping layer 116 in the bottom portion of thememory stack structure 120P may be removed through the vertical contactrecess 121 and the horizontal contact recess 123. The charge trappinglayer 116 may be removed by a wet-etch process. When the charge trappinglayer 116 includes a nitride, the wet-etch process may include achemical capable of etching the nitride.

By removing the charge trapping layer 116, the horizontal length of thehorizontal contact recess 123 may be increased.

Subsequently, the tunnel dielectric layer 117 in the bottom portion ofthe memory stack structure 120P may be removed through the verticalcontact recess 121 and the horizontal contact recess 123. The tunneldielectric layer 117 may be removed by a wet-etch process. When thetunnel dielectric layer 117 includes an oxide, the wet-etch process mayinclude a chemical capable of etching the oxide.

By removing the tunnel dielectric layer 117, the horizontal length ofthe horizontal contact recess 123 may be increased.

While the process of removing the source sacrificial layer 104, theprocess of removing the first liner layer 103, the process of removingthe blocking layer 115, the process of removing the charge trappinglayer 116, the process of removing the tunnel dielectric layer 117 areperformed as described above, the sacrificial sealing layer 122 mayserve as an etch barrier for protecting the dielectric layers 111 and113 and the sacrificial layer 112.

The outer wall of the bottom portion of the channel layer 118 of thememory stack structure 120P may be exposed by the processes of expandingthe horizontal contact recess 123.

The first multi-layer stack in which one or more horizontal contactrecesses 123 are formed may be denoted by 110S′. The remaining secondliner layer 105′ may be referred to as a carbon-containing liner layer.

A contact opening penetrating through the first multi-layer stack 110S′and the second multi-layer stack 120M may be formed through a series ofthe processes illustrated in FIGS. 16 to 20. The contact opening mayinclude a vertical contact recess 121 and a horizontal contact recess123. The horizontal contact recess 123 may extend from the verticalcontact recess 121. The vertical contact recess 121 may extend in adirection (e.g., a vertical direction) perpendicular to the surface(e.g., the top surface) of the lower structure 101, and the horizontalcontact recess 123 may extend in a direction (e.g., a horizontaldirection) parallel to the surface of the lower structure 101. Thehorizontal contact recess 123 may have a high aspect ratio that isparallel to the surface of the lower structure 101. The vertical contactrecess 121 may have a high aspect ratio that is perpendicular to thelower structure 101.

Subsequently, processes similar to those shown in FIGS. 7 to 14 may beperformed over the resulting structure shown in FIG. 20. Hereinafter,descriptions will be given with reference to FIGS. 21 to 28.

Referring to FIG. 21, a source contact material 124A may be formed tofill a contact opening, e.g., a vertical recess 121 and a horizontalcontact recess 123. The source contact material 124A may include aconductive material. The source contact material 124A may includepolysilicon. The source contact material 124A may include phosphorus(P)-doped polysilicon. The source contact material 124A may includecarbon-containing polysilicon. The source contact material 124A mayinclude a stack of phosphorus-doped polysilicon (SiP) and carbon-dopedpolysilicon (SiC).

Subsequently, the source contact material 124A may be selectivelyremoved. The selective removal of the source contact material 124A mayinclude a recessing process, and the recessing process may include awet-etch process. As a result of performing the wet-etching process onthe source contact material 124A, a source contact layer 124 may beformed in the horizontal contact recess 123. The source contact layer124 may partially fill the horizontal contact recess 123. For example,the source contact material 124A may be etched such that the sourcecontact layer 124 is self-aligned to the sidewall of the sacrificialsealing layer 122, and thus the bottom of the vertical recess 121 maydirectly contact the lower source layer 102. The source contact layer124 may remain in the horizontal contact recess 123, and the sourcecontact layer 124 may not remain in the vertical recess 121.

Although not illustrated, the source contact layer 124 may subsequentlybe exposed to an oxidation process. The oxidation process may includedry oxidation or wet oxidation. An edge of the source contact layer 124may be oxidized by the oxidation process. As a result, a barrier oxide(not shown) may be formed at the edge of the source contact layer 124.The barrier oxide may include silicon oxide. The barrier oxide mayprotect the source contact layer 124 from being attacked during thesubsequent process.

The first multi-layer stack 110S′ in which the source contact layer 124is formed may be simply referred to as a source-level stack 110. Thesource level stack 110 may be disposed below the second multi-layerstack 120M, and the source contact layer 124 may be directly coupled tothe channel layer 118 of the memory stack structure 120P.

As described above, the source-level stack 110 which is formed by aseries of processes of replacing the source sacrificial layer 104 withthe source contact layer 124 may have a structure in which the sourcecontact layer 124 is embedded.

Referring to FIG. 22, the sacrificial layers 112 of the secondmulti-layer stack 120M may be selectively removed. As a result,horizontal gate recesses 125 may be formed between the dielectric layers111. Since the sacrificial layer 112 includes nitride, the sacrificiallayer 112 may be removed by a chemical including phosphoric acid(H₃PO₄). While the sacrificial layer 112 is removed, the sacrificialsealing layer 122 may also be removed at the same time. According toanother embodiment of the present disclosure, the sacrificial sealinglayer 122 may be removed after the sacrificial layer 112 is removed.

While the sacrificial layer 112 is removed, the source contact layer 124may be sufficiently protected by a barrier oxide. The barrier oxide mayserve as a protective layer for protecting the source contact layer 124from being attacked.

The horizontal gate recesses 125 may be continuous from the verticalcontact recess 121. Portions of the blocking layer 115 of the memorystack structure 120P may be exposed by the horizontal gate recesses 125.

After the horizontal gate recesses 125 are formed in the secondmulti-layer stack 120M in FIG. 21, a first intermediate multi-layerstack 120′ may be formed. The first intermediate multi-layer stack 120′may have a structure in which the dielectric layers 111 and thehorizontal gate recesses 125 alternate. The horizontal gate recess 125may also be formed between the top dielectric layer 113 and theneighboring dielectric layer 111 as well.

Referring to FIGS. 23 and 24, the gate electrodes 127 may fill thehorizontal gate recesses 125, respectively. In order to form the gateelectrodes 127, a gate material layer 126 may be deposited to fill thehorizontal gate recesses 125 (see FIG. 23). After the gate materiallayer 126 is formed, a second intermediate multi-layer stack 120″ may beformed. The second intermediate multi-layer stack 120″ may have astructure in which the dielectric layers 111 and the gate material 126alternate, and the gate material 126 may cover the sidewalls of thevertical contact recesses 121.

Subsequently, as illustrated in FIG. 24, the gate electrodes 127 may beformed by performing an etch-back process on the gate material layer126. The gate electrodes 127 may include a low resistance material. Thegate electrodes 127 may include a metal-based material. The gateelectrodes 127 may include a metal, a metal silicide, a metal nitride,or a combination thereof. For example, the metal may include nickel,cobalt, platinum, titanium, tantalum, or tungsten. The metal silicidemay include nickel silicide, cobalt silicide, platinum silicide,titanium silicide, tantalum silicide, or tungsten silicide. The gateelectrodes 127 may include a stack of titanium nitride and tungsten.

The ends 127R of the gate electrodes 127 may have a shape that ishorizontally recessed from the ends of the dielectric layers 111. Theends 127R of the gate electrodes 127 may be exposed by the verticalcontact recesses 121. The gate electrodes 127 may not contact the secondliner layer 105′, the lower source layer 102, and the source contactlayer 124.

After the gate electrodes 127 are formed, an alternating stack 120 maybe formed. The alternating stack 120 may have a structure in which thedielectric layers 111 and the gate electrodes 127 are stackedalternately. The memory stack structure 120P may penetrate through thealternating stack 120, and the vertical contact recesses 121 maypenetrate through the alternating stack 120.

The source-level stack 110 may include a lower source layer 102, asource contact layer 124, and a second liner layer 105′, and the bottomportion of the vertical contact recess 121 may not penetrate the lowersource layer 102. Hereinafter, the second liner layer 105′ may be calleda carbon-containing liner layer 105′.

Referring to FIG. 25, the surface of the vertical contact recesses 121may be sealed. The surface of the vertical contact recesses 121 may besealed by a sealing layer 128S. The sealing layer 128S may include oneor more protrusions 128P, and the protrusions 128P may seal the ends127R of the gate electrodes 127. The sealing layer 128S may seal thesides of the dielectric layers 111 and 113. The sealing layer 128S mayseal the side of the source contact layer 124. The sealing layer 128Smay seal the side of the carbon-containing liner layer 105′ and may sealthe exposed surface of the lower source layer 102. The sealing layer128S may include a silicon oxide-based material. The sealing layer 128Smay include a low dielectric material. The low dielectric material mayhave a lower dielectric constant than silicon nitride. The material ofthe sealing layer 128S may have a dielectric constant that is lower thanapproximately 7.

The sealing layer 128S may be thinner than the dielectric layers 111 and113 and the gate electrode 127. The sealing layer 128S may be a layer ofa material that is different from the material of the dielectric layers111 and 113. The sealing layer 128S may be a layer of a material that isdifferent from that of the gate electrode 127. The sealing layer 128Smay include a material having a high wet-etch resistance. The wet-etchresistance of the sealing layer 128S may be obtained from carbon. Thesealing layer 128S may be formed of a carbon-containing material, andthe dielectric layers 111 and 113 may be formed of a carbon-freematerial. The dielectric layers 111 and 113 may be formed of carbon-freesilicon oxide, and the sealing layer 128S may be formed ofcarbon-containing silicon oxide. For example, the dielectric layers 111and 113 may be formed of SiO₂ and the sealing layer 128S may be formedof SiCO. SiCO may be more etch-resistant than SiO₂. The carbon contentof SiCO may be less than the silicon content and the oxygen content. Forexample, SiCO may have a composition ratio of silicon (Si) 34 at %,oxygen 40 at %, and carbon 17 at %. SiCO may have a lower dielectricconstant than silicon nitride (Si₃N₄).

The sealing layer 128S may be formed to have a thickness ofapproximately 50 Å to 100 Å. The high wet-etch resistance of SiCO mayreduce the thickness of the sealing layer 128S. As a result, the size ofeach of the vertical contact recesses 121 for separating cell blocks maybe reduced, which eventually leads to decreased chip size. In acomparative example, when a sealing layer is formed of SiO₂, the sealinglayer should be formed to have a thickness of approximately 150 Å orthicker in consideration of loss in the subsequent processes (e.g., acleaning process). The thick SiO₂ sealing layer of the comparativeexample may make it difficult to fill the vertical contact recesses withsource contact plugs without voids, and each of the vertical contactrecesses of the comparative example should have a relatively large sizein order to improve the gap-fill characteristics of the source contactplugs. On the contrary, since SiCO of the sealing layer 128S accordingto an embodiment of the present disclosure has a higher wet-etchresistance than SiO₂, the sealing layer 128S may be formed thinner thanthe sealing layer of SiO₂ in the comparative example. Therefore, eventhough the size of the vertical contact recesses 121 is small, thevertical contact recesses 121 may be filled with source contact plugswithout voids.

According to another embodiment of the present disclosure, the sealinglayer 128S may include a material that is wet-etch resistant withrespect to the subsequent processes. The sealing layer 128S may includeSiCN, SiBCN, SiBN, or a combination thereof. The wet-etch resistance ofthe sealing layer 128S may be obtained from carbon, nitrogen, boron, ora combination thereof.

According to another embodiment of the present disclosure, a seed layermay be formed prior to the formation of the sealing layer 128S. The seedlayer may form a thin silicon oxide layer or a thin silicon nitridelayer. By forming the seed layer, the conformality of the sealing layer128S may be improved.

According to another embodiment of the present disclosure, the sealinglayer 128S may include a stack of one or more carbon-free silicon oxidelayers and one or more carbon-containing silicon oxide layers. Forexample, after thinly depositing a carbon-free silicon oxide layer, acarbon-containing silicon oxide layer may be deposited over thecarbon-free silicon oxide layer. The carbon-free silicon oxide mayimprove the conformality of the carbon-containing silicon oxide as theseed layer.

Referring to FIG. 26, the sealing layer 128S may be selectively removedto expose the surface of the lower source layer 102. As a result, asealing spacer 128 may be formed on the sidewall of the vertical contactrecess 121. The bottom portion of the sealing spacer 128 maysubstantially completely cover the side of the source contact layer 124and the side of the carbon-containing liner layer 105′. The sealingspacer 128 may include one or more protrusions 128P, and the protrusions128P may seal the ends 127R of the gate electrodes 127. The sealingspacer 128 may seal the sides of the dielectric layers 111 and 113.

The sealing spacer 128 may be vertically continuous along the stackingdirection of the dielectric layers 111 and the gate electrodes 127. Fromthe perspective of a top view, the sealing spacer 128 may have a closedloop-shape that seals the sidewalls of the vertical contact recesses121.

Since the thickness of the sealing layer 128S is thin, the open area ofthe bottom surface of the vertical contact recess 121 may be increasedin an etch process for forming the sealing spacer 128. As a result, itis possible to secure an electrically low resistance and processstability.

After the sealing spacer 128 is formed, a post-cleaning process may beperformed.

Referring to FIGS. 27 and 28, the vertical contact recesses 121 may befilled with a conductive contact material. For example, a source contactplug 132 may be formed in each vertical contact recess 121. The sourcecontact plugs 132 may fill the vertical contact recesses 121. Each ofthe source contact plugs 132 may include a stack of a silicon-containingmaterial 129 and a metal-containing material 131, and it may furtherinclude a barrier material 130 between the silicon-containing material129 and the metal-containing material 131. The silicon-containingmaterial 129 may include polysilicon, and the metal-containing material131 may include tungsten. The barrier material 130 may include titaniumnitride. According to another embodiment of the present disclosure, thesource contact plugs 132 may be formed of tungsten alone.

The silicon-containing material 129 may be formed by depositingpolysilicon to fill the vertical contact recesses 121 and thenperforming an etch-back process on the polysilicon. A pre-cleaningprocess may be performed before the deposition of the polysilicon, and apost-cleaning process may be performed after the etch-back process ofthe polysilicon. The silicon-containing material 129 may be in contactwith the sealing spacer 128.

After the silicon-containing material 129 is formed, the barriermaterial 130 may be conformally deposited. A pre-cleaning process may beperformed before the deposition of the barrier material 130. After theconformal deposition of the barrier material 130, the remainder of thevertical contact recess 121 may be filled with the metal-containingmaterial 131. After the barrier material 130 and the metal-containingmaterial 131 are sequentially deposited, a planarization process usingChemical Mechanical Polishing (CMP) may be performed. As a result, thebarrier material 130 and the metal-containing material 131 may remainonly inside the vertical contact recess 121. The barrier material 130may be in direct contact with the sealing spacer 128, and themetal-containing material 131 may not contact the sealing spacer 128.

Although a plurality of cleaning processes are performed during theprocess of forming the sealing spacer 128, the process of forming thesilicon-containing material 129, and the process of depositing thebarrier material 130, thickness loss of the sealing spacer 128 mayhardly occur.

As described above, the source-level stack 110 and the alternating stack120 may be formed over the lower structure 101. The source-level stack110 may include a lower source layer 102, a source contact layer 124,and a carbon-containing liner layer 105′. The alternating stack 120 maybe formed by alternately stacking the dielectric layers 111 and the gateelectrodes 127. The memory stack structure 120P may completely penetratethrough the alternating stack 120 and may not completely penetratethrough the source-level stack 110. The bottom portion of the memorystack structure 120P may penetrate through the carbon-containing linerlayer 105′ and the source contact layer 104 of the source-level stack110, but may not penetrate through the lower source layer 102. The outerwall of the bottom portion of the channel layer 118 of the memory stackstructure 120P may directly contact the source contact layer 124. Thechannel layer 118, the lower source layer 102, and the source contactplug 132 may be electrically connected through the source contact layer124.

The gate electrodes 127 and the source contact plug 132 may beelectrically disconnected by the sealing spacer 128. The gate electrodes127 and the source contact plug 132 may be physically disconnected bythe sealing spacer 128. A high voltage may be repeatedly applied betweenthe gate electrode 127 and the source contact plug 132, which increasesGBB. This is called a Grown Bad Block phenomenon. According to theembodiment of the present disclosure, the GBB defects may be preventedby forming the sealing spacer 128 including a carbon-containingmaterial. In other words, since the sealing spacer 128 is formed of amaterial having a high wet-etch resistance, thickness loss of thesealing spacer 128 may not substantially occur during the subsequentcleaning processes. Thus, the sealing spacer 128 may be formed thickenough to withstand the high voltage applied between the gate electrode127 and the source contact plug 132.

Also, since the sealing spacer 128 is formed of a low dielectricmaterial, the parasitic capacitance between the gate electrodes 127 andthe source contact plugs 132 may be reduced.

Also, according to an embodiment of the present disclosure, since thecarbon-containing liner layer 105′ is formed of SiCO, there is nosignificant thickness loss by a wet-etch chemical, and the thicknessloss of SiCO caused during the process of forming the horizontal contactrecesses 123 and the process of expanding the horizontal contactrecesses 123 (i.e., a dry etch process and a wet-etch process forremoving the blocking layer 115, the charge trapping layer 116, and thetunnel dielectric layer 117) is so small that the breakdown voltage (BV)characteristics with the source contact plugs 132 may be improved.

In addition, when the carbon-containing liner layer 105′ is formed ofSiCO, the bottom dielectric layer 111 may be formed relatively thin(e.g., approximately 200 Å). Thus, the dopant diffusion movementdistance from the source contact layer 124 to the channel layer 118adjacent to the bottom gate electrode 127 may be shortened. As shown inFIG. 2, when the stack of the second liner layer 105 and the uppersource layer 106 is applied, the dopant diffusion movement distance maybe approximately 450 Å (the bottom dielectric layer of approximately 300Å+the upper source layer of approximately 150 Å). In contrast, when onlythe second liner layer 105′ is applied, the dopant diffusion movementdistance may be approximately 300 Å (the bottom dielectric layer 111 ofapproximately 200 Å+the second liner layer 105′ of approximately 100 Å).

Referring to FIGS. 16 to 28, a method for fabricating a verticalsemiconductor device may include: forming a first multi-layer stack 110Sthat includes a sacrificial source layer 104 and a carbon-containingliner layer 105′ over a lower structure 101; forming a secondmulti-layer stack 120M in which dielectric layers 111 and sacrificiallayers 112 are alternately stacked over the first multi-layer stack110S; forming a memory stack structure 120P that includes a channellayer 118 extending to penetrate through the second multi-layer stack120M and the first multi-layer stack 110S; forming a vertical contactrecess 121 extending to penetrate through the second multi-layer stack120M and the first multi-layer stack 110S by being spaced apart from thememory stack structure 120P; forming a horizontal contact recess 123 byselectively removing the sacrificial source layer 104 through thevertical contact recess 121; expanding the horizontal contact recess 123to expose the lower outer wall of the channel layer 118; filling theextended horizontal contact recess 123 with the source contact layer124; replacing the sacrificial layers 112 with the gate electrodes 127;forming a sealing spacer 128 that seals sidewalls of the verticalcontact recess 121 over the source contact layer 124 and the gateelectrodes 127; and forming a source contact plug 132 in the verticalcontact recess 121. The carbon-containing liner layer 105′ and thesealing spacer 128 may be formed of carbon-containing silicon oxide.

Carbon-containing silicon oxide, i.e., SiCO, may be applied to theprocess of forming contact plugs in DRAMs, logic devices, and the like.For example, after contact etch process for forming a contact hole in aninter-layer dielectric layer is performed, a SiCO spacer may be formedon the sidewall of the contact hole by depositing SiCO and performing anetch-back process. After the SiCO spacer is formed, the contact hole maybe filled with a conductive contact plug. The SiCO spacer may be exposedto a plurality of cleaning processes such as a post-cleaning after theSiCO spacer is formed, a post-cleaning before the conductive contactplug is formed, and the like. Even though the SiCO spacer is exposed tothe subsequent cleaning processes, since the SiCO spacer is a materialwith a high wet-etch resistance, there may be little thickness loss.

According to embodiments of the present disclosure, electricalcharacteristics may be improved as a sealing spacer is formed of amaterial having a high wet-etch resistance between the gate electrodesand the source contact plugs.

According to embodiments of the present disclosure, it is possible toform a sealing spacer to be thick enough to withstand the high voltageapplied between a gate electrode and a source contact plug.

According to embodiments of the present disclosure, since a sealingspacer is formed of a low dielectric material, the parasitic capacitancebetween the gate electrodes and the source contact plugs may be reduced.

According to embodiments of the present disclosure, reliability of avertical semiconductor device may be improved.

While the present disclosure has been described with respect to thespecific embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the disclosure as defined in the followingclaims.

What is claimed is:
 1. A method for fabricating a semiconductor device,comprising: forming a source sacrificial layer over a lower structure;forming a multi-layer stack in which dielectric layers and sacrificiallayers are alternately stacked over the source sacrificial layer;forming a memory stack structure that includes a channel layer and amemory layer, the memory stack structure extending to penetrate throughthe multi-layer stack and the source sacrificial layer; forming avertical contact recess that is spaced apart from the memory stackstructure and extends to penetrate through the multi-layer stack and thesource sacrificial layer; exposing a lower outer wall of the channellayer by selectively removing the source sacrificial layer and a lowerportion of the memory layer of the memory stack structure through thevertical contact recess; forming a source contact layer that surroundsthe lower outer wall of the channel layer; replacing the sacrificiallayers of the multi-layer stack with gate electrodes to form analternating stack; forming a sealing spacer to seal a sidewall of thevertical contact recess over the source contact layer and the gateelectrodes; and forming a source contact plug in the vertical contactrecess, wherein the sealing spacer includes a stack of a layer ofcarbon-free silicon oxide and a layer of carbon-containing siliconoxide, and the carbon-containing silicon oxide is in direct contact withthe source contact plug.
 2. The method of claim 1, wherein thecarbon-containing silicon oxide having a wet-etch resistance greaterthan that of the dielectric layers.
 3. The method of claim 1, whereinthe carbon-free silicon oxide includes SiO₂.
 4. The method of claim 1,wherein the carbon-containing silicon oxide includes SiCO, and a carboncontent of SiCO is less than a silicon content and an oxygen content. 5.The method of claim 1, wherein an outer wall of the source contact plugis surrounded by the sealing spacer, and wherein the sealing spacerextends vertically to cover the gate electrodes, the dielectric layers,and the source contact layer, the gate electrodes and the dielectriclayers being stacked vertically.
 6. The method of claim 1, wherein thesealing spacer includes one or more protrusions extending in a specificdirection to seal one or more ends of the gate electrodes, respectively,the specific direction being perpendicular to a direction in which thegate electrodes and the dielectric layers are stacked.
 7. The method ofclaim 1, wherein the sealing spacer has a thickness of approximately ina range from 50 Å to 100 Å.
 8. The method of claim 1, wherein thesemiconductor device further comprises: a lower source layer between thelower structure and the source contact layer; and an upper source layerbetween the alternating stack and the source contact layer, wherein eachof the upper source layer and the lower source layer include asemiconductor material.
 9. The method of claim 1, wherein the sourcecontact plug includes: a silicon-containing material pattern that fillsa lower portion of the vertical contact recess; a metal-containingmaterial pattern disposed over the silicon-containing material, and abarrier material layer disposed between the silicon-containing materialand the metal-containing material.
 10. The method of claim 1, furthercomprising: a liner layer between the alternating stack and the sourcecontact layer, wherein the liner layer and the carbon-containing siliconoxide include the same material.
 11. The method of claim 10, wherein theliner layer and the carbon-containing silicon oxide include SiCO. 12.The method of claim 10, wherein the dielectric layers of the alternatingstack include a bottom dielectric layer, the remaining dielectric layersof the alternating stack disposed over the bottom dielectric layer, thebottom dielectric layer having a thickness thinner than that of each ofthe remaining dielectric layers.
 13. The method of claim 1, furthercomprising forming a lower source layer over the lower structure, thesource sacrificial layer disposed over the lower source layer, whereinforming the sealing spacer comprises: forming a sealing layer over thedielectric layers, the gate electrodes, and the source contact layer,and the lower source layer; and removing a portion of the sealing layerto expose the lower source layer.
 14. The method of claim 1, furthercomprising: forming a lower source layer over the lower structure;forming a first liner layer over the lower source layer; forming asecond liner layer over the source sacrificial layer; and forming anupper source layer over the second liner layer, wherein the sourcesacrificial layer disposed between the first liner layer and the secondliner layer, and wherein the multi-layer stack disposed on the uppersource layer.
 15. The method of claim 14, wherein the first liner layer,or the second liner layer, or both include a silicon oxide or a SiCO 16.The method of claim 14, wherein the first liner layer includes a siliconoxide, and the second liner layer includes SiCO.
 17. The method of claim1, further comprising: forming a lower source layer over the lowerstructure; forming a first liner layer over the lower source layer; andforming a second liner layer over the source sacrificial layer, whereinthe source sacrificial layer disposed between the first liner layer andthe second liner layer, wherein the multi-layer stack disposed on thesecond liner layer, and wherein the first liner layer is formed of asilicon oxide, and the second liner layer is formed of SiCO.
 18. Amethod for fabricating a semiconductor device, comprising: forming afirst multi-layer stack including a first liner layer, a second linerand a source sacrificial layer disposed between the first liner layerand the second liner layer; forming a second multi-layer stack includingdielectric layers and sacrificial layers over the first multi-layerstack; forming a vertical contact recess extending through the secondmulti-layer stack and the source sacrificial layer; replacing the sourcesacrificial layer with a source contact layer; forming a sealing spaceron sidewall of the vertical contact recess; replacing the sacrificiallayers with conductive layers; and forming a source contact plug in thevertical contact recess, wherein the sealing spacer includes a stack ofa layer of SiO₂ and a layer of SiCO, and the SiCO is in direct contactwith the source contact plug.
 19. The method of claim 18, furthercomprising: after forming the second multi-layer stack, forming a memorystack structure that includes a channel layer and a memory layer, thememory stack structure extending to penetrate through the secondmulti-layer stack and the source sacrificial layer.
 20. The method ofclaim 18, wherein forming the source contact plug in the verticalcontact recess comprising: forming a silicon-containing materialpattern; forming a barrier material layer over the silicon-containingmaterial pattern; and forming a metal-containing material pattern overthe barrier material.